Flexographic printing system

ABSTRACT

A wipe roll and an engraved ink transfer roll of a flexographic printing assembly are suspended from a frame to permit movement of the axis of the wipe roll and the ink transfer roll with respect to the axis of the print cylinder. A first force is continuously applied to the transfer roll. A second force is intermittently exerted on the transfer roll and is capable of overriding the first force to urge the surface of the transfer roll into an ink transfer relationship with the print cylinder. The wipe roll can be mounted for movement with the engraved transfer roll to maintain the desired clearance between these two rolls during the movement of the transfer roll away from and towards the print cylinder.

FLEXOGRAPHIC PRINTING SYSTEM [751 Inventors: Theodore J. Hartka.Phoenix;

William C. Stuley, Ruxton, both of Md.

[73 I Assignec: Wm. C. Staley Machinery C0rp.,

Hunt Valley, Md.

[221 Filed: Oct. 6, 1971 21 Appl. No.: 186,978

[52] U.S. Cl. 101/350, 101/352 [51] Int. C1. B411 31/06, B41f 31/36 [58]Field of Search ..10l/349352, 363, 364,

[ 56] I References Cited UNITED STATES PATENTS 1,975,681 10/1934 Brawnl0l/351 2,333,962 11/1943 Terry 4. 101/351 2,614,492 10/1952 Brodie101/426 X 2,606,520 8/1952 Hoel 101/351 X 3,343,484 9/1967 Dahlgren101/148 3,404,625 lO/1968 White 101/148 3,417,693 12/1968 Hartka....101/364 3,433,155 3/1969 Norton 101/349 3,507,215 4/1970 Shuhmann,101/351 1 Oct. 2, 1973 3,673,959 7/1972 Jezuit 101/148 FOREIGN PATENTSOR APPLlCATlONS 1,238,046 4/1967 Germany [01/364 741,781 5/1943 Germany101/351 Primary EXamim'rJ. Reed Fisher A!l0rneyFinnegan, Henderson &Farabow [57] ABSTRACT A wipe roll and an engraved ink transfer roll of aflexographic printing assembly are suspended from a frame to permitmovement of the axis of the wipe roll and the ink transfer roll withrespect to the axis of the print cylinder A first force is continuouslyapplied to the trans- 4 Claims, 5 Drawing Figures United States Patent 1111 3,762,323

Hartka et al. 1 Oct. 2, 1973 PATENIED 21973 3.762.323

SHEET 1 UF 5 FIG. 1

INVENTORS THEODORE J HARTKA WlLLIAM C. STALEY T NTE 21975 3.762.323

SHEET 2 [1F 5 INVENTORS THEODORE J. HARTKA WILLIAM C. STALEY SHEET 30F 5INVENTORS THEODORE J. HARTKA PATENTEDUEI 2 I973 WILLIAM C. STALEYPATENTED flcI 2 197a SHEET l 0F 5 1N VENTORS J H ART KA THEODORE WILLIAMC. STALEY PAIENIED 2W 3.762.323

sum 5 OF 5 mag '39 HEODORE J. HARTKA WILLIAM C. STALEY FLEXOGRAPHICPRINTING SYSTEM FIELD OF THE INVENTION This invention relates to amethod and apparatus useful .in flexographic printing. Moreparticularly, the invention relates to a method of adjusting theposition of an engraved ink transfer roll with respect to a printcylinder, and to an improved flexographic printing assembly.

BACKGROUND OF THE INVENTION The flexographic printing process utilizeswater base ink which permits easy equipment clean up. Because of themagnitude of the cost savings that result from the ease of clean up,printers have shown considerable interest in converting existingoil-base ink equipment to the flexographic process.

Typically, the conversion of existing oil-base printing equipment to theflexographic process has involved mounting the wipe roll and theengraved ink transfer roll on a mounting frame, and holding these rollsand the mounting frame in a fixed relationship with the print cylinder.This conversion technique has required that exact tolerances bemaintained during installation in the fielda difficult operation.Further, the need to maintain precise tolerances has required'the use ofa heavy, cumbersome roll support structure. Because the wipe roll andthe engraved transfer roll are also heavy, it has been difficult andundesirable to convert larger installations, for example, installationshaving a printing roll of 184 inches in length, to the flexographicsystem since such installations are typically situated in buildings thatlack overhead crane facilities. The weight problem has also tended torestrict the use of the flexographic process in new installations wherea long print cylinder is required.

Also, there has existed a need for an improved method and apparatus foradjusting and maintaining the position of the wipe roll and the inktransfer roll relative to each other and to the print roll duringprinting operations, and for moving the ink transfer roll from the printroll when printing operations terminate.

BRIEF DESCRIPTION OF THE INVENTION The invention provides a method ofadjusting the position of an engraved ink transfer roll with respect to'a print cylinder. The transfer roll is suspended so that its axis canmove in an arcuate path of movement with respect to the print cylinderwith the axis of the transfer roll remaining parallel to'the axis of theprint cylinder. A first force is continuously exerted on thetransferro'll and tends to "move the axis of the transfer roll a'longthearcuate path and to move the surface of the transfer roll out of contactwith the print cylinder. A second force is intermittently applied to thetransfer roll that is capable of overriding the first force to urge.thesurface of the transfer roll into ink transfer contact'with theprint cylinder, with the release of the second force permitting thefirstforc'e to move the transfer'roll out of contact with theprint'c.ylinder.

In preferred embodiments, the method "of the invention includes thesteps of suspending a wipe roll soithat its axis can move in an arcuatepath'ofmovem'ent relative to the print cylinderwith the axis of the'wipe roll remaining parallel to'the axis of the'ptint cylinder,andholding the distance between the axisof the wipe roll and theaxis ofthe'transfer roll a predetermined constant distance apart duringmovement of the transfer roll along its arcuate path.

Also, it is preferred to limit the arcuate movement of the axis of thetransfer roll towards the print cylinder by applying a blocking forcethat acts on the transfer roll when the transfer roll achieves apredetermined position in its travel towards the print cylinder.

In another embodiment, the invention provides a flexographic printingassembly for supplying ink to a print cylinder. The assembly includes aframe held in fixed position with respect to the print cylinder. A pairof spaced pivot arms are pivotally mounted on oppos' ing sides of theframe for pivotal movement about a first axis. An engraved transfer rollis provided having each end rotatably mounted on one of the pivot arms.The axis of the transfer roll is movable in an arcuate path with respectto the print cylinder due to the pivotal mounting of the pivot arms. Apair of spaced wipe arms are pivotally mounted on the frame for movementabout a second axis parallel to the first axis. A wipe roll is providedhaving each end rotatably mounted on one of the wipe arms.

The assembly further includes adjustment means, such as a pair oflength-adjustable tie members, for adjusting and maintaining the nipbetween the wipe roll and the transferroll. Each of the tie members ispivotally mounted on one of the wipe arms and pivotally mounted on oneof the pivot arms. Stop means are mounted on the frame for limiting thepivotal movement of the pivot arms and the approach of the transfer rolltowards the print cylinder.

The position of the transfer roll and the wipe roll are adjusted andmaintained by (a) a force applying means, for example, resilient meanssuch as a compression spring for exerting on the pivot arms a firstmoment arm that is capable of pivoting the pivot arms to move thetransfer roll out of ink transfer relationship with the print cylinder;and (b) releasable actuating .means for exerting a second moment arm onthe pivot arms that can overcome the first moment arm and .thus rotatethe pivot arms into engagement with the stop means .to

hold the transfer roll in ink transfer relationship with the printcylinder during printing operations, with the release of the actuatingmeans permitting the resilient means to move the transfer roll outofcontact with the print cylinder.

Supply means are provided for .feeding ink to the nip formed by the wiperoll and the engraved transfer roll, and drive meansmay be provided torotate the :transfer roll .and the 'wipe .roll.

The invention provides an assembly which permits easy conversion in thefield :of an .o'il-base ink installation to the flexographic process.The conversion .can be effected without the need to establish precisetolerances,b'ecause the apparatus formountingzthe .rollsihas a 'built-inadjustment capability. The assembly 10f the invention isalso desirablyincorporatedintoznewz flexographic printing installations such asprlinterfslotters .used in making corrugated iboxes.

The assembly permits conversion of even ;relatively long printingcylinders 10 :the flexographic process, hecause there is a lessened needfor .amassive frame to rolls can be removed separately.

The adjustment means preferably includes tieing members which permit thenip adjustment between the wipe roll and the engraved transfer roll tobe easily made during assembly. Operating adjustment of the nip ispreferably accomplished by suspending the wipe arms from a shaft mountedfor eccentric rotation relative to the frame, and by varying theposition of the shaft.

The engraved ink trnasfer roll mounting arrangement permits movement ofthis roll away from the print cylinder during cessation of printingoperations, and then movement back into ink-transferring relationshipwith a minimum of operator adjustment. Further, in preferred embodimentsof the invention, the adjustment between the wipe roll and the transferroll is not disturbed when the transfer roll is moved away from theprint cylinder.

The invention consists of the novel methods, parts, constructions,arrangements, combinations, and improvements shown and described. Theaccompanying drawings which are incorporated in and constitute a part ofthis invention, illustrate certain embodiments and, together with thedescription, serve to explain the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS Of the drawings:

, FIG. I is a schematic perspective view of a flexographic printingassembly;

FIG. 2 is a side elevation view of one embodiment of the flexographicprinting assembly of this invention with some elements of the frame notshown for ease of viewing;

FIG. 3 is a vertical section taken along line 33 of FIG. 2 and showingmore elements of the frame and drive means than are illustrated in FIG.2, and omitting the print cylinder for ease of viewing;

FIG. 4 is a vertical section taken along line 44 of FIG. 2 and showingmore elements of the frame and drive means than are illustrated in FIG.2; and

FIG. 5 is a side elevation view of another embodiment of theflexographic printing assembly of this invention with some elements ofthe frame not shown for ease of viewing.

DETAILED DESCRIPTION OF THE INVENTION FIGS. 1-4 illustrate aflexographic printing assembly constructed in accordance with theinvention. FIGS. 1

and 2 show such an assembly installed for use with a print cylinder thatis rotatably mounted on a main frame 12 (not shown in FIGS. 1 and 2, butillustrated in FIGS. 3 and 4). The assembly includes as major componentsa wipe roll 14, an engraved ink transfer roll 16, and a subframegenerally 18 (FIG. 2) from which wipe roll 14 and transfer roll 16 aresuspended. Subframe 18 is rigidly attached to main frame 12 and is thusheld in a fixed position with respect'to print cylinder 10.

In accordance with the invention, a pair of spaced pivot arms areprovided which are pivotally mounted on opposing sides of the frame forpivotal movement about a first axis. As here embodied and as illustratedin FIG. 3, a pair of spaced pivot arms 20 are mounted on pivot pins 22for pivotal motion about the axis of pivot pins. Pivot pins 22 aremounted in a fixed position on subframe 18.

In accordance with the invention, an engraved transfer roll is rotatablymounted between the pivot arms,

and thus is suspended so that its axis can move in an arcuate path intoand out of ink transfer contact with the print cylinder.

In the embodiment of FIGS. 2-4, and as best shown in FIG. 3, the ends ofengraved ink transfer roll 16 are rotatably mounted in journal boxes 24mounted on pivot amrs 20. A suitable engraved ink transfer roll is soldunder the registered trademark Anilox by the Interchemical Corporation.

Engraved transfer roll 16 is driven by the drive train of the printcylinder so that its surface rotates at the speed of the surface of theprint cylinder. As illustrated in FIG. 3, a drive shaft 26 extends fromthe transfer roll 16 through one pivot arm 20, through an opening 27 inmain frame 12, through a journal housing 28, and extends into an overrumclutch 30. Power is transmitted to shaft 26(a) from an idler gear 32,mounted on bracket 34 that is suspended from housing 28, (b) to atransfer roll gear 36 that is driven by idler gear 32, (c) from transferroll gear 36 to overrun clutch 30, and (d) from clutch 30 to shaft 26.The lower end of bracket 34 is fixed on the frame by a torque nut (notshown).

Idler gear 32 is driven by a second idler gear (not shown) that, inturn, is driven by a gear mounted on the axis of the print cylinder.Overrun clutch 30 prevents shaft 26 from exerting torque on gear 36during a cessation of printing operations as explained in more detailbelow.

In accordance with the invention, a pair of spaced wipe arms arepivotally mounted on the frame. The wipe arms suspend a wipe roll sothat the wipe roll forms a nip with the ink transfer roll as seen inFIG. 2. Preferably, the wipe arms are mounted and dimensioned tomaintain the distance between these two rolls the same even when thetransfer roll is moved away from the print cylinder. Thus, readjustmentof the clearance between the ink transfer roll and the wipe roll isusually unnecessary even after a shutdown of printing operations and theautomatic movement of the ink transfer roll away from the printcylinder.

As illustrated in FIG. 4, a pair of spaced wipe arms 40 are pivotallymounted on a pair of spaced lengths 41 of adjusting shaft 42. Lengths 41are mounted for eccentric rotation relative to frame 18 as describedbelow. The axis 44 of lengths 41 is offset from the axis 46 of a pair ofhorizontally aligned eccentric housings 50 and 52. Eccentric housings 50and 52 are fixed on shaft 42 for rotation therewith and are rotatablymounted relative to frame 18 by bearings 53. Thus, torque exerted on ahandwheel 48 will act through a conventional drive train generally 54including a flexible coupling 56 to adjust the position of axis 44,about which wipe arms 40 pivot, with respect to transfer roll 16. Itshould be noted that eccentric housing 50 forms one hub of flexiblecoupling 56.

In accordance with the invention, adjustment means are provided foradjusting and maintaining a nip between said wipe roll and said transferroll. In the embodiment of FIGS. 2-4, the adjustment means comprise apair of length-adjustable tie members 58. As illustrated in FIG. 2, eachtie member 58 is pivotally mounted on a pin 60 on one wipe arm 40 andpivotally mounted on a pin 62 on an adjacent pivot arm 20. Theadjustment means also includes eccentric adjusting shaft 42 on whichwipe arms 40 are pivotally mounted as described above. Eccentricadjusting shaft 42 permits making operating adjustments to change theink film thickness on the engraved roll.

As illustrated in FIG. 2, the distance between the axis of said transferroll 16 and the axis of pivot pin 22, and the distance between the axisof wipe roll 14 and the axis of shaft 42 are substantially equal, andthe distance between (a) the pivot axis 61 of each tie member 58 aboutthe pivot arm 20 on which it is mounted, and the axis of pivot pin 22,and (b) the distance between the pivot axis 63 of each tie member 58about the wipe arm 40 on which it is mounted and the axis of shaft 42are substantially equal. Further, the distance between the axis of shaft42 and the axis of pin 22 and the distance between axes 61 and 63 issubstantially equal. The above-described arrangement helps maintain theproper nip relationship between the transfer roll and the wipe roll.

In accordance with the invention, stop means are provided for limitingthe pivotal motion of the pivot arms and for thus limiting the approachof the transfer roll towards the print cylinder. In the embodimentillustrated in FIGS. 2-4, and as seen in FIG. 3, the stop means areposition adjustable and comprise wear collars 68 concentrically mountedon an adjusting shaft 72 (described in detail below). A bolt 64 ismounted on each pivot arm 20 with bolts 64 engaging wear collars 68, tolimit pivotal movement of the pivot arms.

One end of shaft 72 extends through an eccentric coupling hub 74 and theother end extends through an eccentric hub 76 as seen in FIG. 3. Hubs 74and 76 are aligned and are fixed on shaft72 for rotation therewith. Theaxis of revolution 78 of the'hubs is spaced from the axis of revolution80 of shaft 72.

Coupling hub 74 forms part of a flexible coupling generally 82 and isrotatably mounted on frame 18 by bearing 83, with hub 76 being rotatablymounted on frame 18 by bearing 84 as illustrated in FIG. 3. Coupling 82is rotated by a miter-gear assembly 86 that, in turn, is driven by ahandwheel (not shown) for adjustment purposes. Thus, shaft 72 is mountedfor eccentric rotation relative to frame 18.

In accordance with the invention, force applying means are provided forexerting on the pivot arms a first moment arm that is capable ofpivoting the pivot arms and moving the transfer roll out of ink transferrelationship with the print cylinder; and releasable actuating means areprovided'for exerting a second moment arm on the pivot arms. The secondmoment arm is made capable of overcoming the first moment arm to rotatethe pivot arms into engagement with the stop means and thus hold thetransfer roll in fixed relationship with the print cylinder duringprinting operations. The release of the actuating means permits theforce applying means to movethe transfer roll out of contact with theprint cylinder.

In the embodiment of FIGS. 2-4, the force applying means comprises aresilient means and specifically a pair of compression spring assembliesgenerally 90, with one assembly 90 interposed between each wipe arm 40and each pivot arm 20 and seated therebetween as illustrated in FIG. 2."Spring assembly 90 exerts a force on projection 92 of pivot arm 20 thattends to pivot arm 20 in a clockwise direction about pivot pin 22 andthus tends to move transfer roll 16 out of contact with print cylinder.Spring assembly 90 also exerts a force on wipe arm 40 with this forcetending to pivot wipe arm 40 in a clockwise direction about eccentricshaft 42.

In the embodiment of FIGS. 2-4, and as illustrated. in, FIG. 2, thereleasable actuating means comprise a pair of air actuators generally 94including a retractable ram 96 that can be urged into contact with pivotarm 20 to exert a releasable force on the pivot arm. The releasableforce exerts a releasable moment arm that rotates pivot arm 20 in acounterclockwise direction into engagement with the stop means, andspecifically wear collar 68 (illustrated in FIG. 3). Ram 96 can beretracted to permit spring assembly to rotate pivot arm 20 in aclockwise direction and thus move transfer roll 16 to the left and up,and out of ink transfer contact with print cylinder 10.

In accordance with the invention, ink supply means are provided forfeeding ink to the nip formed by the wipe roll and the engraved inktransfer roll. As here embodied and as schematically illustrated in FIG.1, the ink supply means is conventional and comprises a pump 100, asupply tank 102, an ink feed line 104 for supplying ink to a nozzle 106,collection means 108 for collecting ink that overflows the ends oftransfer roll 16 and wipe roll 14, and a return line 110 connectingcollection means 108 and pump 100. Ink is constantly circulated tonozzle 106 by pump 100 and recirculated to the pump by gravity flow.

With reference to FIG. 4, it can be seen that drive means are providedfor driving wipe roll 14 independently of the drive train of the printcylinder. (The print cylinder drive train drives transfer roll 16 asdescribed above.) Wipe roll 14 is driven by a motor 112 (illustrated inFIG. 1) that is rigidly mounted on frame 18. A conventional drive train1 14 is provided for transmitting torque from the motor 112 to aflexible coupling 116 mounted on a stub shaft 118 which extends fromwipe roll 14. Motor 112 normally drives wipe roll l4v both duringprinting operations and during short interruption in the rotation of theprint cylinder. Thus, wipe roll 14 and transfer roll 16, due to itsfrictional contact with wipe roll 14, continue to rotate during such aninterruption, and are maintained in a state of readiness for theresumption of printing operations.

Overrun clutch 30 prevents rotation of transfer roll 16, due tofrictional engagement with wipe roll 14, from driving print cylinder 10when torque is not being transmitted from the main drive system to printcylinder 10 as illustrated in FIG. 3.

In the embodiment illustrated in FIGS. 2-4, ,a disengage stop means ismounted on the frame for engaging the pivot arms and limiting thepivotal motion of the transfer roll away from the print-cylinder. Inpractice, the stop means are usually adjustedso the transfer roll clearsthe print cylinder by about l/8 inch. As illustrated in FIG. 2, the stopmeans comprises a'threaded bolt 120 that is mounted in a threadedopening of element 122 of frame 18. The position of bolt 120 is thusadjusted by advancing or retracting the threaded bolt in the threadedopening.

FIG. I schematiclaly illustrates the operation of a flexographicprinting system. Sheets to, be printed are fed to the nip formed by rolland cylinder '10having a printing die 132 mounted thereon. Ink istransferred to the printing dieby engraved ink transferroll 16 whichforms a nip with wipe roll 14, which preferably is a rubber roll.

In the flexographic process, hydraulic pressure on the ink, generatedmainly by the dynamic flow of ink along the roll contact area, iscompensated by the contact pressure between wipe roll 14 and engravedtransfer roll 16 to regulate the ink film thickness on transfer roll 16.

A roll adjusting procedure which can be used in the assembly of theflexographic printing system of FIGS. 2-4 will now be described. Asillustrated in FIG. 2, the force of gravity urges transfer roll 16towards print cylinder by tending to cause pivot arms to rotate in acounterclockwise direction. Similarly, gravity urges transfer arms 40 topivot in a counterclockwise direction in the absence of other forces.Thus, gravity will tend to align the rolls in the position shown in FIG.2.

The length of tie members 58 is adjusted with eccentric shaft 42 in amid position to permit wipe roll 14 and engraved transfer roll 16 totouch. The adjustable stop means, eccentric shaft 72 having wear collars68 mounted thereon, is positioned to limit the travel of engravedtransfer roll 16 toward the surface of print cylinder 10.

Each spring assembly 90 is capable of exerting an adjustable amount offorce on the pivot arm 20 and the wipe arm 40 it engages becausethreaded bolt 124, extending through a threaded opening in wipe arm 40,and seated on plate 126 can advance and retract the plate with respectto projection 92 on pivot arm 20. During the roll adjusting procedure,spring assembly 90 is adjusted to provide a sufficient force to rotatethe rolls l4 and 16 and arms 20 and 40 away from print cylinder 10. i

The disengage stop means are adjusted to limit the travel of the rollsl4 and 16 away from print cylinder 10. This is a screw adjustment madeby advancing or retracting bolt 120 in the threaded opening in frameelement 122.

Operating adjustments of the roll psoitions can be accomplished asdescribed below. The thickness of the film of ink on engraved transferroll 16 is controlled by rotating adjusting shaft 42 by means of forcetransmitted by an adjusting handwheel (not shown) that rotates mitergear assembly 86 and flexible coupling 82 which is coupled to shaft 42.

Adjustment of the transfer of ink to the printing die is accomplished byrotating eccentric shaft 72 which changes the clearance tolerancebetween the printing die mounted on pivot cylinder 10 and transfer roll16 by stopping the actuator-induced movement of the transfer rolltowards print cylinder 10 at the desired position.

In starting up a printing operation, air actuator 94 forces rolls 14 and16 towards print cylinder 10and into an operating position. In forcingrolls 14 and 16 towards the print cylinder, the moment arm exerted byactuator 94 overcomes the moment arms exerted by spring assembly 90 onrolls l4 and 16.

By releasing air pressure acting on actuator 94, the spring forcesexerted by spring assembly 90 pivot arms 20 and 40 and move rolls l4 and16 until pivot arm 20 engages stop means 120. At this time, the entireassembly has retracted and is spaced clear of the printing die.

The unique mounting arrangement and linkage is arranged so that therelative position and adjustment of wipe roll 14 and engraved transferroll 16 are not significantly changed by the controlled movement towardsor away from the printing die. Thus, these rolls do not need to be resetor readjusted before resumption of printing.

FIG. 5 illustrates another embodiment of the invention in which a wiperoll 14 and an engraved transfer roll 16 are rotatably mounted,respectively, on the lower end of a pair of wipe arms 40 and the lowerend of a pair of pivot arms 20. Arms 40 and arms 20 are, respectively,pivotally mounted on pivot pins 124 and 126. Pivot pins 124 and 126 areattached to frame elements (not shown) and are held in a fixed positionrelative to print cylinder 10. It should be understood that FIG. 5illustrates the mounting arrangement at one end of rolls 14 and 16, andthat the mounting arrangement at the other end of the rolls isidentical.

In the embodiment of FIG. 5, the axis of transfer roll 16 is movable inan arcuate path with respect to print cylinder 10 due to the pivotalmovement of pivot arms 20. The center of gravity of transfer roll 16exerts about pivot pin 126 a momentarm, which is passive for reasonsdiscussed below, that tends to move the surface of transfer roll 16 in aclockwise direction towards print cylinder 10. The center of gravity ofwipe roll 14 exerts a first moment arm about pivot pin 124 that moveswipe roll 14 in a counterclockwise direction towards transfer roll 16.

Through the mounting arrangement of rolls 14 and 16 on their respectivearms 40 and 20, and the relationship of the axes of rolls l4 and 16 withtheir respective pivot pins 124 and 126, the first moment arm is madecapable of overcoming the passive moment arm. When wipe roll 14 is incontact with transfer roll 16, the first moment arm moves transfer roll16 out of contact with print cylinder 10.

The adjustment means of the embodiment of FIG. 5 include a pair ofadjustable spring loaded tie bars 138. Each tie bar 138 is rigidlyattached to the upper end of pivot arm 20. A contact plate 140 having anopening therethrough for insertion of tie bar 138 is seated against wipearm 40 by a spring 142. Tie bar 138 thus exerts a force producing amoment arm acting in a clockwise direction on wipe arm 40 and inopposition to the counterclockwise first moment arm caused by gravityaction on wipe roll 14 and wipe arms 40. Tie bar 138 exerts a forceproducing a moment arm acting in a clockwise direction that tends toturn pivot arm 20 in a clockwise direction about pin 126, and inopposition to the passive moment arm resulting from gravity acting ontransfer roll 16 and pivot arms 20. Each tie bar 138 exerts an equalmoment arm on wipe arm 40 and pivot arm 20 since it applies an equalforce to each arm and the forces are applied at an equal distance fromthe pivot axis of each arm. The amount of force exerted by tie bar 138can be adjusted by advancing or retracting a threaded nut 139 along thethreaded tie bar to vary the force exerted by spring 142. The adjustmentmeans also includes a wipe arm pivot stop as described below.

Stop means are provided for limiting the pivotal movement of pivot arms20 in a clockwise direction, and thus limiting the approach of transferroll 16 towards print cylinder 10. The stop means comprises a pair ofposition-adjustable brackets 144, each having a cylindrical stop member148 mounted thereon. Bracket 144 is pivotally mounted on frame 18 by pin150. An adjusting screw 154 which is rotatably mounted on frame 18 isseated against each bracket 144 to prevent clockwise rotation of thebrackets when a pivot arm 20 is rotated in a clockwisedirection intovcontactwith a stop member 148.

A pair of wipe arm pivot stops comprise part of the adjustment means ofthe embodiment of FIG. 5. Each pivot stop is mounted on pivot arm 20 andcomprises a bracket 146 that is pivotally mounted on pivot arm 20 by pin152, and a stop member 148 mounted on each bracket 146 that preventsclockwise rotation of wipe arm 40 past a defined adjustable point. Theposition of bracket 146 relative to pivot arm 20 can be adjusted byadjusting screw 154 which is rotatably mounted in threaded engagementwith a bracket 155 extending from pivot arm 20.

The force applying means of the embodiment of FIG. comprises themounting-arrangement of transfer roll 16 and pivot arms'20, and'wiperoll 14 and wipe arms 40 in relation to print cylinder 10. As describedabove, the illustrated mounting arrangement results in a gravity-inducedmoment arm that acts on pivot arms 20 to urge transfer roll 16 to movein a counterclockwise di' rection and out of contact with print cylinder10.

A pair of air actuators 156 exert a second moment arm on each pivot arm20 with the second moment arm urging pivot arms 20 into engagement withstop member 148 to hold transfer roll 16in fixed ink transferrelationship with print cylinder during printing operations. Retractionof ram 158 by release of air pressure to actuator 156 permits thegravity-induced moment arm that constantly acts on pivot arms whentransfer roll 16 is in contact with wipe roll 14 to move transfer roll16 out of ink transfer contact with print cylinder 10.

Disengage stop means comprising a pair of threaded bolts 160 areprovided for engaging pivot arms 20 and limiting the movement oftransfer roll 16 away from print cylinder 10 upon release of the forceapplied by actuator 156.

Operatingadjustment of the contact relationship between rolls 14 and 16,and roll 16 and print cylinder 10 in the embodiment of FIG. 5 isprovided by eccentric adjusting shafts 162 and 164, respectively.

Eccentric shaft 164 extends between pivot arms 20 and is mounted on thepivot arms for eccentric rotation relative to the pivot arms. It iseccentric shaft 164 that contacts stop member 148 when the pivot arm 20is pivoted in a clockwise direction. Thus, adjustment of the position ofeccentric shaft 164 adjusts the distance between transfer roll 16 andprint cylinder 10, and the transfer of ink to the printing die.

Similarly, eccentric shaft 162 extends between wipe arms 40 and ismounted on the wipe arms for eccentric rotation relative to the wipearms. Eccentric shaft 162 constitutes part of the adjusting means formaking operating adjustments on the nip between wipe roll 14 andtransfer roll 16. Adjustment of the position of eccentric shaft 162,which contacts stop member 148 attached on arm 20, adjusts the positionof wipe roll 14 relative to transfer roll 16.

Preferably, eccentric shafts 162 and 164 can be rotated byoperator-controlled hand wheels (not shown in FIG. 5) which operate adrive train similar to that illustrated in FIG. 4.

In the embodiment of FIG. 5, the drive means for wipe roll 14 is a motorthat drives wipe roll 14 through a structure similar to that illustratedin FIG. 4 for driving the wipe roll in that embodiment, and the drivemeans for engraved transfer roll 16 =comprisesa gear and clutcharrangement as illustrated in FIG. 3.

The invention in its broader aspects is not limited to the specificdetails shownand described. Departures;

pivotally mounted on opposing sides of said frame for pivotal movementabout a first axis;

C. an engraved transfer roll having eachend rotat ably mounted on thelower end of one of said pivot arms, theaxis of said transfer roll beingmovable in an arcuate path with respect to the print cylinder due to thepivotal mounting of saidvpivot arms with the center of gravity of saidtransfer roll exertinga passive moment arm tending to move saidvtransferroll towards the print cylinder;

D. a pair of spaced wipe arms pivotally mounted on said frame formovement about a second axis parallel to said first axis;

E. a wipe roll having each end rotatably. mounted on the lower end ofone of said wipe arms, the center of gravity of said wipe roll exertinga first moment arm that moves said wipe roll into contact with saidtransfer roll with said first moment arm capable of overcoming saidpassive moment arm when said wipe roll and said transfer roll are incontact to thereby move said transfer roll out of contact with saidprint cylinder;

F. a pair of adjustable spring-loaded tie bars, each of said tie barsconnecting the upper end of one of said wipe arms and the upper end ofone of said pivot arms for exerting on each of said one wipe arm andsaid one pivot arm a force creating a moment arm that opposes thegravity-induced moment arm applied to the respective wipe arm and pivotarm;

G. stop means mounted on said frame for engaging said pivot arms tolimit the pivotal movement. of said pivot arms and thus limit theapproach of said transfer roll towards said print cylinder;

H. releasable actuating means for exerting a releasable second momentarm on said pivot arms that can overcome said first moment arm and thusto,- tate said pivot arms into engagement with said stop means to holdsaid transfer roll in fixed ink transfer relationship with the printcylinder during printing operations, with the release of said actuatingmeans permitting said first moment arm to move said transfer roll out ofcontact with the print cylinder; and

I. supply means for feeding ink to the nip formed by the wipe roll andthe engraved transfer roll.

2. The printing assembly of claim 1 including an cecentric shaftextending between said pivot arms, and mounted on said pivot arms foreccentric rotation relative to said pivot arms, said eccentric shaftengaging said stop means mounted on said frame, for adjusting thedistance between said transfer roll and said print cylinder duringprinting operations.

4. The printing assembly of claim 1 including a disengage stop meansmounted on said frame for engaging said pivot arms and limiting thepivotal motion of said transfer roll away from the print cylinder uponrelease of said actuating means.

1. A flexographic printing assembly for supplying ink to a printcylinder comprising: A. a frame held in fixed position with respect tothe print cylinder; B. a pair of spaced pivot arms, said pivot armsbeing pivotally mounted on opposing sides of said frame for pivotalmovement about a first axis; C. an engraved transfer roll having eachend rotatably mounted on the lower end of one of said pivot arms, theaxis of said transfer roll being movable in an arcuate path with respectto the print cylinder due to the pivotal mounting of said pivot armswith the center of gravity of said transfer roll exerting a passivemoment arm tending to move said transfer roll towards the printcylinder; D. a pair of spaced wipe arms pivotally mounted on said framefor movement about a second axis parallel to said first axis; E. a wiperoll having each end rotatably mounted on the lower end of one of saidwipe arms, the center of gravity of said wipe roll exerting a firstmoment arm that moves said wipe roll into contact with said transferroll with said first moment arm capable of overcoming said passivemoment arm when said wipe roll and said transfer roll are in contact tothereby move said transfer roll out of contact with said print cylinder;F. a pair of adjustable spring-loaded tie bars, each of said tie barsconnecting the upper end of one of said wipe arms and the upper end ofone of said pivot arms for exerting on each of said one wipe arm andsaid one pivot arm a force creating a moment arm that opposes thegravity-induced moment arm applied to the respective wipe arm and pivotarm; G. stop means mounted on said frame for engaging said pivot arms tolimit the pivotal movement of said pivot arms and thus limit theapproach of said transfer roll towards said print cylinder; H.releasable actuating means for exerting a releasable second moment armon said pivot arms that can overcome said first moment arm and thusrotate said pivot arms into engagement with said stop means to hold saidtransfer roll in fixed ink transfer relationship with the print cylinderduring printing operations, with the release of said actuating meanspermitting said first moment arm to move said transfer roll out ofcontact with the print cylinder; and I. supply means for feeding ink tothe nip formed by the wipe roll and the engraved transfer roll.
 2. Theprinting assembly of claim 1 including an eccentric shaft extendingbetween said pivot arms, and mounted on said pivot arms for eccentricrotation relative to said pivot arms, said eccentric shaft engaging saidstop means mounted on said frame, for adjusting the distance betweensaid transfer roll and said print cylinder during printing operations.3. The printing assembly of claim 2 including an eccentric adjustingshaft extending between said wipe arms, and mounted on said wipe armsfor eccentric rotation relative to said wipe arms, said eccentricadjusting shaft engaging said stop means on said pivot arms forpermitting the operating adjustment of the nip between said transferroll and said wipe roll.
 4. The printing assembly of claim 1 including adisengage stop means mounted on said frame for engaging said pivot armsand limiting the pivotal motion of said transfer roll away from theprint cylinder upon release of said actuating means.